The present invention relates to an adjustable seatbelt energy management device. More particularly the present invention relates to an adjustable seatbelt energy management device utilizing a polarizable fluid such as a magnetorheological fluid.
As is well known, safety-belts are used for securing the occupants of motor vehicles and aircraft firmly in their seats when the vehicle or aircraft undergoes abnormal acceleration in the transverse direction or deceleration in the direction of travel. It is also known that ideally the safety-belts should not be rigidly secured but should be capable of yielding in a controlled manner. For example, when a collision occurs in the direction of travel, resulting in a force from deceleration and the weight of the traveler, it is beneficial to the safety of the traveler to have the safety-belt dissipate some of the energy. The present invention utilizes a novel energy management system employing polarizable fluids such as magnetorheological fluids (hereinafter "MR" fluids).
MR fluids, such as ferromagnetic fluids, are suspensions of small magnetizable particles (normally a metal such as iron) in a fluid (normally an oil). The magnetizable particles align themselves with reference to an applied magnetic field. The degree of alignment is proportional to the strength of the magnetic field. This particle alignment will effect the viscosity of the fluid. Normally, MR fluids are free flowing fluids with a viscosity similar to oil. When a magnetic field is applied the viscosity will increase, almost to the point of a solid, due to particles forming a dense network of particle chains. The degree of change is proportional to the magnitude of the applied magnetic field. MR fluids also react very rapidly to the applied magnetic field. The response time of MR fluids is on the order of a few milliseconds and is useful in speed dependant applications such as the control of a seat belt restraint during a collision.
MR fluids are superior to other polarizable fluids, such as electrorheological fluids (hereinafter "ER fluids"), in applications of the present invention because they are much stronger, stable, and easier to use. MR fluids are 20-50 times stronger than ER fluids and may be operated using low voltage sources such as a 12 volt car battery. MR fluids are also far less susceptible to contaminants and extremes in temperature than ER fluids. MR fluids are utilized in the preferred embodiments of the present invention.